The present invention relates to deformable sleeves in general, and more particularly to a deformable sleeve for use as the flow-controlling element in a pinch valve. Still more particularly, the present invention relates to a pinch valve including the deformable sleeve.
Various constructions of pinch valves are already known. Usually, a pinch valve includes two pinching elements, such as pinching bars, which are mounted on a support for movement toward and away from one another. In many instances, it is sufficient when only one of the pinching elements is movable, while the other is stationarily mounted on the support, which may be either stationary, or movable, relative to the pipeline in which the pinch valve is incorporated. A deformable sleeve of an elastically deformable material, such as gum rubber, Neoprene, Butyl, Buna N, Hypalon, Viton, urethane, EPT (nordel), silicone, or food grade rubber, is situated between and interconnects and communicates the ends of two sections of the pipeline in which the pinch valve is interposed. The sleeve extends across the space between the pinching elements, so that it is squeezed by the latter as they move relative to one another in direction toward each other, whereby the flow-through cross-sectional area of, and thus the amount of the flowable medium passing between the sections of the pipeline through, the sleeve is reduced. Conventional pinch valves have been traditionally used for controlling the flow of media which are conveyed at relatively low pressures, such as solids in suspension, that is slurries or air-propelled particulate materials, abrasive materials such as metal ores, asbestos fibers, sand, sugar, coal, wood chips, pulp, paper stock, plastic pellets, sewage, talc, cement, fly ash, and various chemicals and foodstuffs. The reason for this limitation as to the type of materials conveyed was that the elastomeric sleeve of the conventional pinch valve constructions was unable to withstand high internal pressures needed for conveying other types of materials, especially over substantial distances.
However, the requirement for maintaining the internal pressure in the sleeve as low above the atmospheric pressure as possible resulted in other kinds of problems, especially in the problem of loss of elasticity of the sleeve after an extended period of dwell thereof in the closed position. This is attributable to the gradual creep of the elastomeric material of the sleeve, so that the material loses its tendency to return to its original shape corresponding to the open position of the pinch valve and the maximum flow-through cross-sectional area of the sleeve. To avoid this drawback, it has been proposed in the U.S. Pat. No. 4,172,580 to mount wire loops on the pinching elements, these wire loops embracing or being partially embedded in the sleeve and being operative for exerting oppositely oriented forces on the sleeve at opposing locations situated between the pinching elements, during the movement of such pinching elements apart. As the distance between such locations is reduced due to the application of such forces thereto, the sleeve is gradually restored to its original cylindrically tubular configuration corresponding to the open position of the sleeve, in response to the movement of the pinching elements away from one another.
A considerable advantage of a pinch valve is not only its simple construction, but also the absence therefrom of any interfaces between relatively movable elements which would have to be sealed in order to prevent leakage of the medium present in the pipeline therethrough to the exterior of the valve, as they have to be in other types of valves. Thus, it would be advantageous if pinch valves could be used for controlling the flow of high-pressure media as well. However, as already alluded to before, the conventional sleeves are incapable of withstanding such high pressures. Experience has shown that, because of its elasticity, the sleeve of a conventional pinch valve will bulge out or assume a balloon-shaped configuration, which strains the material of the sleeve and may lead to its rupture. Yet, it was heretofore believed to be impossible to so reinforce the sleeve as to prevent its outward bulging, since it was believed that this would automatically prevent the inward deformation of the sleeve which is to occur during the pinching operation of the pinch valve.